The Fiesta is the smallest car Ford sells in the United States, and now it’s available with the tiniest engine the company has ever made.

Ford's first three-piston motor is a 1.0-liter turbocharged powerhouse with an aluminum block the company says is small enough to fit on a sheet of letter paper or in a piece of carry-on luggage, with room to spare. With it, Ford joins Smart, Mitsubishi and MINI in what’s quickly becoming the year of the three-cylinder.

Rated at 123 horsepower, it has just three more ponies than the Fiesta’s standard 1.6-liter four-cylinder, but it comes with a big jump in tire-twisting torque. It’s rated at 125 lb-ft vs. 112 lb-ft, while a turbo overboost delivers up to 148 lb-ft in 15-second bursts. That’s a lot longer than you’d ever keep your foot planted to the floor in a car with a five-speed manual transmission. Lift, then shift.

The engine is so potent and delivers its punch at such low engine speeds that you can practically idle away from a stop. There’s none of the frantic revving and clutch-slipping commonly required when driving an econobox. This is good, because an automatic transmission isn’t available.

While it’s plenty quick for your commute, the $995 SFE (Super Fuel Economy) option on Fiesta SE and Titanium trims is aimed efficiency, not speed, and has an EPA highway rating of 43 mpg, which is higher than any of Ford’s hybrid models. It drops to 31 mpg around town, but both seem legit in the real world.

The engine can be had in sedan or hatchback styles at a starting price of $17,400 – about $2,500 more than the lowest-priced four-cylinder Fiesta, which has a 38-mpg rating. You won’t make that back at the pump, where it drinks regular unleaded, but the extra power comes with something else: refinement.

Despite its size, the engine has a deep, rich sound without any of the harsh buzz subcompact car owners are familiar with. And thanks to some clever engineering, it’s also much smoother than its odd number of cylinders suggests. Ford intentionally imbalanced the flywheel and crank pulley to offset the off-kilter firing pattern, eliminating the need for the separate counter-rotating balance shaft many small motors use, which keeps the overall package as small and light as possible.

Given that the engine is basically the only difference between the SFE and most Fiestas, the transformation is dramatic. It’s a much more pleasant car, and while it’s no Fiesta ST sports model, it’s not a stretch to call it “fun to drive.”

Most of the drawbacks are those already inherent in the Fiesta, namely its size. Even for the subcompact class, the cabin is a little tight in the rear seats, though the trunk in the sedan is awkwardly large. Sadly, the SFE only comes with low rolling resistance tires on steel wheels fitted with plastic hubcaps – an old-school economy car touch.

Ford offers the 1.0-liter engine in several models overseas, and it’s so confident that it can pull much more than its weight that it’s adding it to the larger Focus compact in the U.S. this fall.

I’m not sure what the math will be like there, but three is definitely greater than four in the Fiesta.